The present invention is related to the field of fiber-to-the-curb (xe2x80x9cFTTCxe2x80x9d) digital loop carrier (xe2x80x9cDLCxe2x80x9d) systems for communicating information in the local access loop between a central office switching station and a plurality of customer locations. In particular, a novel optical network unit (xe2x80x9cONUxe2x80x9d) for use with such an FTTC system is described, in which the ONU includes at least one multi-service common card coupled to a plurality of service cards via a plurality of high-speed serial interconnections. The high-speed serial interconnections are preferably arranged in a separate point-to-point xe2x80x9cstarxe2x80x9d configuration in which each service card includes a separate high-speed point-to-point serial interface with the one or more multi-service common cards. A family of adaptable multi-service common cards and a scalable FTTC system for delivering present and future multi-media services in the local loop are also disclosed.
By eliminating the traditional backplane found in present ONUs, the ONU of the present invention provides a modular, easily-reconfigurable (i.e. adaptable) architecture that extends the operating life of the ONU far beyond that of traditional ONU designs, and thus enables the system to adapt to unknown services that may or may not be anticipated at the time of installation. Due to the inherent limitations of a backplaned ONU, such adaptability to future services is not possible. Using the features and principles of the present invention, a future-proof, expandable FTTC system can be installed that is capable of providing a multitude of multi-media services over a single fiber-optic connection, such as telephony, high-speed data, CATV, video-on-demand, as well as any number of future services that may require extremely high-bandwidth.
In a typical DLC system, the digital transport capabilities of the phone network are extended from the central office switch into a particular neighborhood or business location. A remote digital (xe2x80x9cRDTxe2x80x9d) is placed at a remote location from the central office and is connected to it via a fiber-optic cable, or some other high-bandwidth connection. The remote digital terminal receives PCM-modulated voice information from the central office switch, converts the digital PCM signals into analog voice signals, and routes the analog voice signals to a particular customer location via a plurality of line-cards (or service cards) that connect the RDT to the customer""s equipment. Similarly, the RDT converts analog voice information from the customer to a digital PCM format for transport back to the central office switch. An example of a digital loop carrier system is set forth in U.S. Pat. No. 5,046,067 (xe2x80x9cthe ""067 patentxe2x80x9d), which is assigned to the assignee of the present invention. The teaching of this patent is hereby incorporated into the present application by reference.
An FTTC system is an extended version of the DLC system described above, in which the fiber-optic capabilities are extended further into the local loop by fiber-coupling a plurality of ONU telecommunication terminals to the RDT (which is then referred to as a Host Digital Terminal, or HDT), wherein the ONUs are located very close to the customer locations. An example FTTC system is set forth in FIG. 1, discussed in more detail below. The system shown in FIG. 1 is also described in U.S. patent. application Ser. No. 08/794,723, titled xe2x80x9cDistributed Ethernet Hubxe2x80x9d (the xe2x80x9c""723 applicationxe2x80x9d). This application is commonly assigned to the assignee of the present invention and the teaching of this application is hereby incorporated into this disclosure by reference. As shown in FIG. 1, in a typical FTTC system the RDT is converted into an HDT, which, in many respects, is similar to the RDT, except that the HDT is further connected to a plurality of ONU telecommunication terminals via fiber-optic cable. The HDT includes appropriate circuitry and programming for routing signals to and from the plurality of ONUs and the central office switching station.
The ONUs are relatively small pedestal terminals that are physically located in close proximity to a customer""s location, such as 500xe2x80x2 or less. By placing the ONU in close physical proximity to the customer, high-bandwidth communications can be managed through the ONU over traditional wiretypes. Each ONU typically services a plurality of customers, such as 4 to 8, although, in the future, more customers may be serviced from a single ONU. The ONU provides many functions. It converts optical signals from the HDT into appropriate electrical signals that correspond to the customer""s equipment, such as analog phone signals, or high-speed data signals. It provides voltage surge protection for the physical connections to the customer""s premises, such as twisted-pair copper or coaxial cable. It provides built-in test capabilities so that the lines to the customer""s premises can be tested from the central office. It receives power from the HDT, and converts the received power into a conditioned power level that serves the ONU circuitry, as well as many other functions.
Presently, FTTC systems including ONUs are typically deployed for Plain Old Telephone Service (xe2x80x9cPOTSxe2x80x9d), with the intention of getting fiber-optic cable close to the customer""s premises so that present and future broadband services can be provided as they are defined, or as they become economically feasible. One example of these types of broadband services is high-speed Internet access. The ""723 application provides a solution to delivering these types of services using presently available ONU technology. Other types of broadband services include CATV, video-on-demand, video conferencing, xDSL, interactive television, digital TV and radio, ISDN, as well as many other yet to be defined high-bandwidth applications. Companies seeking to deploy FTTC systems would like to be sure that future services, which have not even been defined, can still be handled by the FTTC system hardware in place. Thus, a future-proof architecture is desirable for the ONU, which provides the critical link between the FTTC system and the customer premesis. Presently known ONUs are not future-proof.
Presently known ONUs are not capable of being future-proof because they utilize a backplane architecture. FIGS. 2A and 2B, discussed in more detail below, set forth such an ONU incorporating a backplane architecture. In these types of ONUs, the common cards and service cards plug into a circuit-board backplane that includes a plurality of connectors for mating to corresponding connectors on the common or service cards and one or more electrical busses that connect the cards together. The one or more busses are metal interconnections (or traces) embedded in the backplane circuit board. The cards communicate with each other primarily via the backplane traces. Because the structure of the backplane inherently limits the services that can be handled by the ONU, any backplane architecture is not capable of being future-proof.
There are many problems associated with using a backplane structure. First, there is no modularity built into the system, since the position and spacing of the backplane connectors is mechanically fixed. Thus, the backplane can only accept circuit cards of a particular dimension and width. Second, the bandwidth of the backplane is limited by its electrical properties. These electrical properties that limit the bandwidth include the impedance of the interconnections between the circuit boards and the backplane and the impedance limitations of the metallization traces that connect the connectors together. In addition, termination resistors may limit the speed of the backplane bus. Because of these physical and electrical limitations, at higher frequencies it becomes very difficult to accurately distribute any type of clocking (or other data) signals over the backplane, due to skewing of the signals that may render the system inoperable.
In summary, it is not feasible to design a backplane ONU that is future-proof. Unless the operator of the FTTC system is willing to retrofit the ONUs with a new backplane every 3 or 4 years (a very unlikely scenario given the large labor and materials costs involved), the entire system is essentially bandwidth-limited by the structure of the ONU backplane the moment it is installed in the field. This is a very undesirable reality for the customer spending millions of dollars to install an FTTC system.
In addition to the drawing figures set forth below, other presently known ONUs are described in U.S. Pat. Nos. 5,500,753 to Sutherland, 5,600,469 to Yamazaki, and 5,303,229 to Withers. Each of these presently known ONU systems includes a backplane architecture and thus suffers from the many disadvantages noted above. See, for example, FIG. 2 of the ""753 patent and FIGS. 1A/1B of the ""469 patent. The ONUs described in these patents are not future-proof, are not readily adaptable, do not provide the ability to handle a multitude of services, and therefore do not satisfy the present need in this field for an ONU capable of being used in an FTTC system for many years into the future.
Thus, there remains a general need in this field for a multi-service, adaptable ONU that does not employ a backplane architecture and thus avoids the many disadvantages associated with designing a future-proof backplane.
There remains a more particular need for such an ONU in which a plurality of different types of service cards can be supported via a single common card.
There remains yet another need for a multi-service FTTC system in which telephony, high-speed data, video and other presently undefined high-bandwidth services can be channeled through an adaptable ONU system without undue costs for retrofitting and installation.
There remains still another need for an ONU in which individual service cards can be replaced in the ONU without effecting the other services provided by the ONU.
There remains still another need for an ONU that can support a family of modular common cards, wherein the common card capabilities build from simple telephony cards to more complex telephony/data/video cards, and beyond.
Still another need remains for a preferred method and structure of interconnecting the one or more common cards and the plurality of service cards in a backplane-less ONU so that bandwidth and flexibility are maximized.
The present invention overcomes the problems noted above and satisfies the needs in this field for a multi-service, adaptable optical network unit for use in a FTTC system. The ONU of the present invention includes a multi-service common card and a plurality of multi-media service cards that are connected to the common card using a card-link interface. The card-link interface is preferably a high-speed LVDS serial-bus connection organized in a star configuration such that each service card is connected to the multi-service common card using a separate point-to-point card-link. By eliminating the traditional backplane structure found in present ONU designs, the present invention provides a scalable, adaptable, future-proof FTTC system that can transport present-day multi-media services as well as yet-to-be-defined future high-bandwidth applications.
One embodiment of the present invention provides a fiber-to-the-curb digital loop carrier system for transporting multi-media information in the local loop between a central office switching station and a plurality of customer locations, comprising: a plurality of host digital terminals coupled to the central office switching station by fiber-optic connections; and at least one optical network unit coupled to a host digital terminal by fiber-optic connections, wherein each optical network unit comprises: at least one multi-service common card including a fiber optic-interface, a service multiplexer, and a plurality of card-link interface circuits; a plurality of service cards including circuitry for processing a particular multi-media service, and at least one card-link interface circuit; and a plurality of card-links coupling the plurality of service cards to the multi-service common card.
Another embodiment of the present invention provides an optical network unit for use in a fiber-to-the-curb system, comprising: a multi-service common card; a plurality of service cards; and a plurality of serial interface connections for communicating information between the common card and the plurality of service cards. The plurality of serial interface connections are preferably connected in a star configuration.
Still another embodiment of the present invention provides a multi-service common card for use in an optical network unit of a fiber-to-the-curb digital loop carrier system, comprising: a fiber optic interface; a service multiplexer; and a plurality of card-link interface circuits.
Another embodiment provides an optical network unit, comprising: a multi-service common card and a plurality of service cards, wherein the multi-service common card includes means for receiving and transmitting optical signals and for converting the optical signals into corresponding electrical signals, means for routing the corresponding electrical signals to the plurality of service cards, and a plurality of card-links for coupling the multi-service common card to the plurality of service cards.
A preferred system-level method of the present invention provides a method of transporting multi-media information in a fiber-to-the-curb digital loop carrier system, comprising the steps of: receiving multi-media information at a central office switching station; converting the multi-media information into optical signals and routing the optical signals to a plurality of host digital terminals via a plurality of fiber optic cables; receiving the multi-media optical signals at the host digital terminals and routing the signals to a plurality of optical network units via a plurality of fiber optic cables; receiving the multi-media optical signals at the plurality of optical network units and converting the signals into corresponding electrical signals; and routing the electrical signals to corresponding multi-media service cards within the optical network unit via a plurality of high-speed serial interface circuits that couple the multi-media service cards to one or more multi-service common cards.
Other embodiments of the present invention will become apparent when reviewing the detailed description of the drawings set forth below.
The present invention provides many advantages over presently known ONUs. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) a future-proof architecture that can accommodate a wide range of applications and services, including those that have yet to be defined, and which can scale from simple telephony, video or data-only applications to a combination of these three services and beyond; (2) no backplane limitations on bandwidth or interconnection; (3) scalable interconnection to support future services; (4) a preferred star interconnection scheme that allows each service card to operate independently from the other service cards and at a variety of speeds; (5) adaptable, modular, flexible, and low cost; (6) low power operation; (7) variable card-spacing enclosure for holding cards of varying degrees of thickness; (8) preferred low-voltage differential signaling (xe2x80x9cLVDSxe2x80x9d) to support scalable high-speed serial interface between the common card(s) and the plurality of service cards; (9) scalable multi-service common card capable of interfacing to a variety of service cards using a plurality of high-speed serial interface connections; and (10) a special-purpose line-card carrier that enables the use of backplane-type service cards with the present invention.